This invention relates to novel multibinding local anesthetic compounds that bind to voltage-gated Na+ ion channels and thereby modulate their activity. The compounds of this invention comprise at least two ligands covalently connected by a linker or linkers, wherein at least one of the ligands in its monovalent (i.e. unlinked) state binds to and is capable of modulating the activity of a voltage-gated Na+ ion channel. The ligands are linked together such that the multibinding compounds thus formed demonstrate a biologic and/or therapeutic effect on processes mediated by voltage-gated Na+ ion channels that is greater than that of the same number of unlinked ligands made available for binding to the channels. In one preferred embodiment, the compounds of the present invention are capable of producing local anesthesia of longer duration than are the corresponding unlinked monovalent ligands. The invention also relates to methods of using such compounds and to methods of preparing them.
These multibinding local anesthetic compounds are particularly useful in treating conditions and diseases that require pain control. Accordingly, this invention also relates to pharmaceutical compositions comprising a pharmaceutically acceptable excipient and an effective amount of a compound of this invention.
State of the Art
Action potentials are generated in nerve and muscle cells by ion currents that pass selectively across plasma membranes through transmembrane ion channels. Local anesthetics exert their effects by specifically binding to Na+ channels, thereby inhibiting Na+ currents and causing the blockade of Na+ channel-dependent impulse conduction. The necessary practical advantage of local anesthetics is that their action is reversible at clinically relevant concentrations and their use is followed by complete recovery of nerve and muscle function with no evidence of damage to nerve fibers or cells.
Ion channels are formed by the association of integral membrane proteins into a structure having a central hydrophilic pore. The structure of the voltage-gated sodium ion channel has been extensively studied (reviewed by W A Catterall, Annu. Rev. Biochem. 64: 493-531 (1995)). The channel consists of a complex of one xcex1- and 2xcex2-subunits. FIG. 1A illustrates the general features of the channel. The xcex1-subunit is the pore-forming subunit, contains a voltage sensor and contains specific binding sites for local anesthetic drugs. This subunit consists of a polypeptide chain with four homologous domains (I-IV), each domain comprising 6 membrane-spanning protein helices (S1-S6). This subunit is flanked at the outer surface of the membrane by two xcex2-subunits, which are heavily glycosylated and which interact with the lipid bilayer in which the channel is embedded. The xcex22 chain is topologically similar to the xcex21 chain, but is not shown in the figure.
Ion channels are characterized by their gating and selectivity properties. Selectivity refers to the rate at which different ion species pass through an open channel under standard conditions. The Na+ channel pore is selectively permeable to Na+, which passes through the channel at rates that are diffusion-limited, and which equilibrates according to the electrochemical gradient across the membrane. Gating is the process that regulates the opening and closing of an ion channel. The voltage-gated Na+ channel opens and closes in response to changes in membrane potential. When the membrane is depolarized (i.e., the membrane potential becomes less negative ), the xe2x80x9crestingxe2x80x9d channel transitions through closed intermediate states to become an xe2x80x9copenxe2x80x9d Na+-conducting channel. With time, the channel closes and becomes xe2x80x9cinactivatedxe2x80x9d (i.e., refractory to reopening ). The channel recovers its ability to respond to a depolarizing stimulus by returning to the xe2x80x9cresting statexe2x80x9d after an interval of time.
There is considerable evidence that the channel itself is a specific receptor for local anesthetics. As mentioned above, the Na+ channel contains specific binding sites for local anesthetic drugs, which exhibit stereoselectivity. FIG. 1B shows a highly schematic representation of the Na+ channel illustrating differences in the binding sites for different classes of Na+ channel modulators and blocking agents, as is currently understood.
The binding sites for neurotoxins, such as saxatoxin and tetrodotoxin (TTX), and scorpion and anemone toxins (ScTx) are thought to be located at the outer mouth of the channel pore. This region includes binding sites for cations, e.g. ammonium ions, as well.
Other, more lipid soluble toxins, such as batrachotoxin (BTX), veratridine, and aconitine, bind within the channel and act to spontaneously open the channel and/or prevent it from closing normally. Current understanding of neuronal sodium channels indicates that binding sites for xe2x80x9cclassicalxe2x80x9d local anesthetics (LA), such as lidocaine, as well as lipophilic quaternary ammonium ion channel blockers, may lie within the internal region of the channel, as shown. This binding site is understood to be allosterically linked to the BTX binding site. Lipophilic binding domains are found at the innermost region of the channel.
It has been suggested that tertiary amine drugs may have two binding sites on the channel, a first site located near the pore that preferentially binds charged species and a second site that binds neutral species. The binding of an anesthetic molecule to the first site would block ion permeation through the pore, while the binding to the second site would act to prevent conformational changes that are required for channel opening (G R Strichartz, Chapter 2, In: Neural Blockade in Clinical Anesthesia and Management of Pain, Third Edition, (M J Cousins and P O Bridenbaugh, Eds.),Lippincott-Raven Publishers, Philadelphia(1998)).
The inhibitory effect of certain local anesthetics is enhanced by membrane depolarization. This effect is attributed to a higher affinity of these local anesthetics for inactivated channels than for resting channels. Repetitive depolarizations potentiate anesthetic activity by xe2x80x9cuse-dependentxe2x80x9d (phasic) block such that an increasing number of channels become stabilized in the non-conducting state.
The duration of action of a local anesthetic is proportional to the time during which it is present at effective concentrations in contact with the nerve, or, more precisely, the ion channel(s). The effect of most currently used local anesthetics tends to be short-lived as a result of dissociation from and diffusion away from the intended site of action; therefore, repeated doses must be administered for a prolonged effect. Undesired side effects of local anesthetics are largely a function of systemic concentrations of the drug resulting from such diffusion. These effects include paralysis of cardiac and smooth muscle systems, or undesired stimulation of the CNS. Because of these serious side effects, the quantity of drug administered must be carefully controlled.
Consequently, local anesthetic compounds having properties that allow effective concentrations to be maintained at the intended local site of action would be useful for prolonging the duration of action, thereby enhancing the clinical utility of local anesthetics in pain management and mitigating untoward toxic effects resulting from systemic concentration of the drug.
This invention provides novel multibinding compounds that are useful as inhibitors of voltage-gated Na+ channels and are effective as local anesthetics. Accordingly, one aspect of this invention is directed to multibinding compounds of Formula I:
(L)p(X)qxe2x80x83xe2x80x83I
and pharmaceutically acceptable salts thereof;
wherein:
each L is a ligand that may be the same or different at each occurrence;
each X is a linker that may be the same or different at each occurrence;
p is an integer of from 2 to 10; and
q is an integer of from 1 to 20;
wherein each of said ligands comprises a ligand domain capable of binding to a voltage-gated Na+ channel of a cell.
Preferably q less than p.
Preferably, each of said ligands is capable of inhibiting the generation and conduction of action potentials by said cell. More preferably, each of said ligands independently comprises a group of Formula (A):
Arxe2x80x94Wxe2x80x94xe2x80x83xe2x80x83(A)
wherein:
Ar represents an aryl, heterocyclyl or heteroaryl group; and W is selected from a covalent bond, xe2x80x94[CR1R2]rxe2x80x94, xe2x80x94[CR1R2]rC(O)xe2x80x94, xe2x80x94C(O)O[CR1R2]rxe2x80x94, xe2x80x94OC(O)[CR1R2]rxe2x80x94, xe2x80x94Oxe2x80x94[CR1R2]rC(O)xe2x80x94, xe2x80x94C(O)xe2x80x94NHxe2x80x94[CR1R2]rxe2x80x94, and xe2x80x94NHxe2x80x94C(O)[CR1R2]r, where r is an integer of 0 to 10, and R1 and R2 are independently H, alkyl, substituted alkyl or a group xe2x80x94NRaRb, where Ra and Rb are both alkyl.
Preferably each divalent linker X is independently selected from a structure of:
(a) Formula II:
xe2x80x94N(R3)xe2x80x94Zxe2x80x94N(R4)xe2x80x94xe2x80x83xe2x80x83(II)
xe2x80x83wherein:
Z is alkylene, substituted alkylene, (alkylene O)w-alkylene where w is an integer of 1 to 10, or alkenylene; and
R3 and R4 are independently hydrogen, alkyl, substituted alkyl, aralkyl, a ligand, an X-ligand group, or R3 and R4 may independently form together with Z and the nitrogen atoms to which they are bound an N-containing heterocyclic ring optionally containing an additional 1 to 4 heteroatoms selected from O, S, SO2, SO, and NRxe2x80x3, where Rxe2x80x3 is a ligand, hydrogen, alkyl or substituted alkyl;
(b) Formula III:
xe2x80x94Yaxe2x80x94Zxe2x80x2xe2x80x94Ybxe2x80x94xe2x80x83xe2x80x83(III)
xe2x80x83wherein:
Zxe2x80x2 is a heterocycle, aryl, heteroaryl, a crown compound having at least two unsubstituted ring nitrogens or a group xe2x80x94NRxe2x80x94, where R is alkyl;
Ya and Yb are independently a covalent bond, alkylene, substituted alkylene, (alkylene-O)w-alkylene where w is an integer of 1 to 10, or xe2x80x94C(O)xe2x80x94(CH2)nxe2x80x94NRxe2x80x94, where R is hydrogen or alkyl and n is an integer of 1 to 10;
(c) Formula IV:
xe2x80x94N+(R3xe2x80x2)(R7)xe2x80x94Zxe2x80x3xe2x80x94N+(R4xe2x80x2)(R8)xe2x80x94xe2x80x83xe2x80x83(IV)
xe2x80x83wherein:
Zxe2x80x3 is alkylene or substituted alkylene; and
R3xe2x80x2, R4xe2x80x2, R7 and R8 are independently alkyl, substituted alkyl, aralkyl, or a ligand, and optionally one of R7 and R8 is not present; and
(d) Formula V:
xe2x80x94Xxe2x80x2xe2x80x94Zxe2x80x2xe2x80x3xe2x80x94(Yxe2x80x2xe2x80x94Zxe2x80x2xe2x80x3)vxe2x80x94Xxe2x80x2xe2x80x94xe2x80x83xe2x80x83(V)
xe2x80x83wherein:
v is an integer of 0 to 20;
Xxe2x80x2 at each separate occurrence is independently alkylene, substituted alkylene, alkenylene, substituted alkenylene, alkynylene, substituted alkynylene, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94S(O)xe2x80x94, xe2x80x94S(O)2xe2x80x94, xe2x80x94NRxe2x80x94, xe2x80x94N+ R Rxe2x80x2xe2x80x94, xe2x80x94C(O)xe2x80x94, xe2x80x94C(O)Oxe2x80x94, xe2x80x94C(O)NRxe2x80x94, xe2x80x94NRC(O)xe2x80x94, xe2x80x94C(S)xe2x80x94, xe2x80x94C(S)Oxe2x80x94, xe2x80x94C(S)NRxe2x80x94 or a covalent bond, where R and Rxe2x80x2 at each separate occurrence are independently as defined below for Rxe2x80x2 and Rxe2x80x3;
Zxe2x80x2xe2x80x3 is at each separate occurrence independently selected from alkylene, substituted alkylene, (alkylene-O)w-alkylene where w is an integer of 1 to 10, alkylalkoxy, cycloalkylene, substituted cycloalkylene, alkenylene, substituted alkenylene, alkynylene, substituted alkynylene, cycloalkenylene, substituted cycloalkenylene, arylene, substituted arylene, heteroarylene, substituted heteroarylene, heterocyclene, substituted heterocyclene, crown compounds, or a covalent bond;
Yxe2x80x2 at each separate occurrence is independently selected from xe2x80x94Oxe2x80x94, NRxe2x80x2, S, xe2x80x94C(O)xe2x80x94(CH2)nxe2x80x94NRxe2x80x2xe2x80x94, xe2x80x94NRxe2x80x2xe2x80x94(CH2)n C(O)xe2x80x94, xe2x80x94NRxe2x80x2xe2x80x94C(O)xe2x80x94NRxe2x80x2xe2x80x94, xe2x80x94Oxe2x80x94C(O)xe2x80x94Oxe2x80x94, xe2x80x94NRxe2x80x2xe2x80x94C(xe2x95x90NRxe2x80x2)xe2x80x94, xe2x80x94C(xe2x95x90NRxe2x80x2)xe2x80x94NRxe2x80x2xe2x80x94, xe2x80x94NRxe2x80x2C(O)xe2x80x94Oxe2x80x94, xe2x80x94Nxe2x95x90C(Xxe2x80x2)xe2x80x94NRxe2x80x2xe2x80x94, xe2x80x94P(O)2(ORxe2x80x2)xe2x80x94Oxe2x80x94, xe2x80x94S(O)nxe2x80x94CRxe2x80x2Rxe2x80x3xe2x80x94, xe2x80x94S(O)nxe2x80x94NRxe2x80x2xe2x80x94, Sxe2x80x94Sxe2x80x94 and a covalent bond; where n is 0, 1, or 2; and
R, Rxe2x80x2 and Rxe2x80x3 at each separate occurrence are selected from hydrogen, alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, alkenyl, substituted alkenyl, cycloalkenyl, substituted cycloalkenyl, alkynyl, substituted alkynyl, aryl, heteroaryl and heterocyclic.
It is understood, of course, that trivalent linkers will have an additional linking point such as shown in FIG. 4.
Preferably, this invention is directed to multibinding compounds of Formula I, wherein p is an integer of from 2 to 4, and q is less than p. Most preferred are multibinding compounds having a structure selected from: 
where Ar and W have the definitions provided above for formula A, and R3, R4 and Z have the meanings given in Formula II above;
(b) Formula Ib
Arxe2x80x94Wxe2x80x94Yaxe2x80x94Zxe2x80x2xe2x80x94Ybxe2x80x94Arxe2x80x83xe2x80x83(Ib)
where Ar and W have the definitions provided above for formula A, and Ya, Yb and Zxe2x80x2 have the meanings given in Formula III above; and 
where Ar and W have the definitions provided above for formula A, and R3xe2x80x2, R4xe2x80x2, R7, R8 and Zxe2x80x3 have the meanings given in Formula IV above.
In presently preferred embodiments, each ligand group Arxe2x80x94Wxe2x80x94 is independently selected from:
2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH((CH2)2CH3)xe2x80x94;
2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94;
(S)-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
(R)-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
o-tolyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
o-tolyl-NHxe2x80x94C(O)xe2x80x94CH(CH3)xe2x80x94;
o-tolyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
4-[xe2x80x94C(O)xe2x80x94Oxe2x80x94(CH2)2xe2x80x94N(CH2CH3)2]-phenyl-;
4-[xe2x80x94C(O)xe2x80x94NHxe2x80x94(CH2)2xe2x80x94N(CH2CH3)2]-phenyl-;
4-[xe2x80x94C(O)xe2x80x94NH(CH3)]-phenyl-;
4-[xe2x80x94C(O)xe2x80x94Oxe2x80x94(CH2)2xe2x80x94N(CH3)2]-phenyl-;
4-[xe2x80x94C(O)xe2x80x94Oxe2x80x94CH2CH3]-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
4-[xe2x80x94C(O)xe2x80x94Oxe2x80x94CH3]-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
4-[xe2x80x94C(O)xe2x80x94Oxe2x80x94CH3]-2-methylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
4-[C(O)xe2x80x94Oxe2x80x94CH3]-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
4-aminophenyl-C(O)xe2x80x94;
4-butylaminophenyl-C(O)xe2x80x94;
2,6-dimethylphenyl-Oxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
phenyl-(CH2)3xe2x80x94;
phenyl-C(O)xe2x80x94(CH2)2xe2x80x94;
4-[xe2x80x94NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94N(CH2CH3)2]-3,5-dimethylphenyl-Oxe2x80x94CH2xe2x80x94C(O)xe2x80x94;
4-aminophenyl-C(O)xe2x80x94Oxe2x80x94(CH2)2xe2x80x94;
4-methoxyphenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
2-methylphenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
phenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
4-chlorophenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
2-methyl-4-methoxyphenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
2-methyl-4-chlorophenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94;
2-methylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH3)xe2x80x94;
2-methylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
phenyl-(CH2)2xe2x80x94C(O)xe2x80x94;
4-nitrophenyl-C(O)xe2x80x94Oxe2x80x94(CH2)2xe2x80x94;
2-chloro-4-nitrophenyl-C(O)xe2x80x94Oxe2x80x94(CH2)2xe2x80x94;
(S)-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(N(CH3)2)xe2x80x94;
(R)-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(N(CH3)2)xe2x80x94;
(S)-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(N(CH2CH3)2)xe2x80x94;
(R)-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CH(N(CH2CH3)2)xe2x80x94;
4-{O-[(CH2)nxe2x80x94C(O)xe2x80x94O]mR}-2,6-dimethylphenyl-NHxe2x80x94C(O)xe2x80x94CHRxe2x80x2xe2x80x94, where n is an integer equal to 1 to 6, m is 0 or 1, R is C1-C6 alkyl, and Rxe2x80x2 is H or alkyl;
2-ethyl-6-methylphenyl-NHxe2x80x94C(O)xe2x80x94CH(CH2CH3)xe2x80x94;
2,4,6-trimethylphenyl-CH(CH2CH3)xe2x80x94C(O)xe2x80x94NHxe2x80x94; and
2-ethyl-6-methylphenyl-NHxe2x80x94C(O)xe2x80x94CH2xe2x80x94.
Preferred multibinding compounds of this invention include by way of example compounds listed in Table 2 (Preferred Embodiments).
Another aspect of the invention is directed to a pharmaceutical composition comprising a pharmaceutically acceptable excipient and a therapeutically effective amount of one or more multibinding compounds represented by Formula I,
(L)p(X)qxe2x80x83xe2x80x83I
and pharmaceutically acceptable salts thereof;
wherein:
each L is a ligand that may be the same or different at each occurrence;
each X is a linker that may be the same or different at each occurrence;
p is an integer of from 2 to 10; and
q is an integer of from 1 to 20;
wherein each of said ligands comprises a ligand domain capable of binding to a voltage-gated Na+ channel of a cell in a mammal, thereby inhibiting the generation and conduction of action potentials by said cell and modulating the diseases and conditions resulting therefrom.
Such compositions are particularly useful for producing local anesthesia in a mammal whereby the multibinding compounds act upon voltage-gated Na+ channels of a nerve and thereby interrupt nerve conduction.
Preferably, the pharmaceutical compositions of this invention comprise one or more multibinding compounds of Formula I, wherein p is an integer of from 2 to 4, and q is less than p. Most preferably, such compositions comprise bivalent multibinding compounds of Formulas Ia, Ib and Ic.
In one of its methods aspects, this invention is directed to a method of preparing a multibinding compound represented by formula I:
(L)p(X)qxe2x80x83xe2x80x83I
wherein
each L is a ligand that may be the same or different at each occurrence;
X is a linker that may be the same or different at each occurrence;
p is an integer of from 2 to 10; and
q is an integer of from 1 to 20;
wherein each of said ligands comprises a ligand domain capable of binding to a voltage-gated Na+ channel of a cell, said method comprising:
(a) providing at least p equivalents of a ligand L or precursors thereof and at least q equivalents of linker or linkers X; and
(b) covalently attaching said ligands to said linkers to produce a multibinding compound; or
(bxe2x80x2) covalently attaching said ligand precursors to said linkers and completing the synthesis of said ligands thereupon, thereby to produce a multibinding compound. Preferably, p is an integer of from 2 to 4, and q is less than p. Most preferably, p is equal to 2.
Another aspect of the invention is directed to a method for producing local anesthesia in a mammal, which method comprises administering to a mammal in need of such treatment a therapeutically effective amount of a pharmaceutical composition comprising a pharmaceutically acceptable excipient and one or more multibinding compounds represented by formula I,
(L)p(X)qxe2x80x83xe2x80x83(I)
and pharmaceutically acceptable salts thereof,
wherein
each L is a ligand that may be the same or different at each occurrence;
X is a linker that may be the same or different at each occurrence;
p is an integer of from 2 to 10; and
q is an integer of from 1 to 20;
wherein each of said ligands comprises a ligand domain capable of binding to a voltage-gated Na+ channel of a cell mediating the conduction of nerve impulses in a mammal, thereby blocking the conduction of said impulses and producing local anesthesia.
A preferred embodiment is the use of pharmaceutical compositions comprising bivalent compounds of Formulas Ia, Ib and Ic and their pharmaceutically acceptable salts to produce local anesthesia of long duration (i.e., from about 6 hours to about 36 hours). In particularly preferred embodiments, these compositions have greatly attenuated or negligible systemic toxicity relative to conventional monovalent (i.e., unlinked) anesthetics.